Olefin polymerisation

Finally, from the dynamics simulations it was found that the Cp rings are very flexible, and during the simulation they are not very closely attached to the metal centre as often anticipated. For further details regarding the metallocene and mono-cyclopentadienyl based olefin polymerisation studied by quantum molecular dynamics simulation we refer to [2] and [8-10]. 

T. DaH-Occo, U. Zucchini, and 1. Cufftani, in W. Kaminsky and H. Sinn, eds.. Transition Metals and Organometallics as Catalystsfor Olefin Polymerisation, Springer-Vedag, Berlin, 1988, p. 209. 

A weU-known feature of olefin polymerisation with Ziegler-Natta catalysts is the repHcation phenomenon ia which the growing polymer particle mimics the shape of the catalyst (101). This phenomenon allows morphological control of the polymer particle, particularly sise, shape, sise distribution, and compactness, which greatiy influences the polymerisation processes (102). In one example, the polymer particle has the same spherical shape as the catalyst particle, but with a diameter approximately 40 times larger (96). 

The principal use of the peroxodisulfate salts is as initiators (qv) for olefin polymerisation in aqueous systems, particularly for the manufacture of polyacrylonitrile and its copolymers (see Acrylonitrile polymers). These salts are used in the emulsion polymerisation of vinyl chloride, styrene—butadiene, vinyl acetate, neoprene, and acryhc esters (see Acrylic ester polymers Styrene Vinyl polymers). 

Organometallic compounds as cata- 30 lysts of olefin polymerisation (70)... 

Abstract Over the past decade significant advances have been made in the fields of polymerisation, oligomerisation and telomerisation with metal-NHC catalysts. Complexes from across the transition series, as well as lanthanide examples, have been employed as catalysts for these reactions. Recent developments in the use of metal-NHC complexes in a-olefin polymerisation and oligomerisation, CO/olefm copolymerisation, atom-transfer radical polymerisation (ATRP) and diene telomerisation are discnssed in subsequent sections. 

A number of highly active ethylene polymerisation catalysts have resulted from the combination of functionalised NHC ligands with Ti, the first of these was the bis(phenolate)carbene ligated complex 3 [8], Upon activation with modified MAO (MMAO), this species gave an activity of 290 kg-mol bar h in the one test reported, making it one of the most active carbene-based olefin polymerisation catalysts known. In later work the same complex was evaluated with straight MAO activation, and activities of up to ca. 100 kg mol -bar" -h" were reported for linear polyethylene production [9],... 

Iron-Based and Cobalt-Based Olefin Polymerisation Catalysts... 

Keywords 2-6-Bis(arylimino)pyridine, Cobalt catalysts, Iron catalysts, Olefin polymerisation, Polyethylene... 

For more general overviews of post-metallocene a-olefin polymerisation catalysts, the reader is referred to a series of reviews [8, 9, 10, 11, 12], while recent reviews pertaining to the importance of 2,6-bis(imino)pyridines and to iron and cobalt systems per se have also been documented [13, 14],... 

Elementary considerations show that of all spectroscopic methods only the UV need be considered for olefin polymerisations. The reasons for the success of this method in the... 

The only studies on olefin polymerisations in methylene dichloride in which kp was deduced directly from the rate of reaction were carried out by Ledwith and his collaborators [9, 13] with extremely low concentrations of monomer and catalyst. They polymerised isobutyl vinyl ether and N-vinyl carbazole in a Biddulph-Plesch calorimeter with trityl or tropylium salts and obtained the first-order rate constants k1 from the conversion curves. Since different catalysts gave the same ratio of kx c they concluded that for each of them Xxr = c0 and hence identified with kp which must in fact be k p, as explained above. It seems unlikely that if several initiators give the same value of kp, they do so because they are all equally inefficient, and the inference that they do so because they are all 100% efficient, i.e., that for all of them x = c0, seems plausible - but it would be useful to have a direct check of this. 

This method has not been used so far for olefin polymerisations, but in fact the only difficulty in its application is that Q must be such that it can be detected in the very low concentrations (10 6 to 10"9 M) which x is believed to have in these reactions, for instance by activation analysis. 

In Section 3 it was shown that for those olefin polymerisations in solvents of DC about 10 which are ionic, propagation must be predominantly by free ions, under the usual polymerisation conditions. For the polymerisations by perchloric acid we can take a concrete numerical example by which it can be shown that ion-pairs (VI) cannot play any important part in the reaction. The relevant dissociation equilibrium is... 

Most of the kp values which seem reasonably reliable are shown in Tables 1 and 2. At first sight the kp values fall into two groups For olefin polymerisations they lie between ca. 103 and 109 M 1 s 1 and for the O- and 5-heterocyclics they lie in the range 10 3 to 10 (with the exception of 1,3-dioxepan). 

It is generally accepted that many olefin polymerisations proceed through carbenium ion chain-carriers, and in these reactions the propagation consists simply of the successive additions of a carbenium ion to the double-bond of the monomer. 

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